1. Field of the Invention
The present invention relates to injectors and nozzles for high temperature applications, and more particularly, to fuel injectors and nozzles for gas turbine engines used in aircraft.
2. Description of Related Art
A variety of devices and methods are known in the art for injecting fuel into gas turbine engines. Of such devices, many are directed to injecting fuel into combustors of gas turbine engines under high temperature conditions.
European Patent Application No. 1,811,229, which is incorporated by reference herein in its entirety, describes several aspects of fuel nozzles for gas turbine injectors. Fuel injectors for gas turbine engines on an aircraft direct fuel from a manifold to a combustion chamber of a combustor. The fuel injector typically has an inlet fitting connected to the manifold for receiving the fuel, a fuel nozzle located within the combustor for spraying fuel into the combustion chamber, and a housing stem extending between and fluidly interconnecting the inlet fitting and the fuel nozzle. The housing stem typically has a mounting flange for attachment to the casing of the combustor.
Fuel injectors are usually heat-shielded because of high operating temperatures arising from high temperature gas turbine compressor discharge air flowing around the housing stem and nozzle. The heat shielding prevents the fuel passing through the injector from breaking down into its constituent components (i.e., “coking”), which may occur when the wetted wall temperatures of a fuel passage exceed 400° F. The coke in the fuel passages of the fuel injector can build up to restrict fuel flow to the nozzle.
Heretofore, injectors have included annular stagnant air gaps as insulation between external walls, such as those in thermal contact with high temperature ambient conditions, and internal walls in thermal contact with the fuel. In order to accommodate differential expansion of the internal and external walls while minimizing thermally induced stresses, the walls heretofore have been anchored at one end and free at the other end for relative movement. If the downstream tip ends of the walls are left free for relative movement, even a close fitting sliding interface between the downstream tip ends can allow fuel to pass into the air gap formed between the walls. This can result in carbon being formed in the air gap, which carbon is not as good an insulator as air. In addition, the carbon may build up to a point where it blocks venting of the air gap to the stem, which can lead to an accumulation of fuel in the air gap. This can lead to diminished injector service life and may require frequent and costly cleaning of the fuel injector.
Such conventional methods and systems generally have been considered satisfactory for their intended purpose. However, there still remains a continued need in the art for a nozzle or fuel injector that allows for differential expansion while reducing or preventing fuel entry in the air gaps. The present invention provides a solution for these problems.